Year: 2026
Type: preprint
Abstract: Thorium-229 doped calcium fluoride ($^{229}$Th:CaF$_2$) is a leading candidate for a solid-state nuclear clock, owing to the unusually low energy of the $^{229}$Th isomer transition at 8.3557\,eV and the very high banggap of CaF$_2$ around 12\,eV. Here we report a temperature-dependent study of $^{229}$Th:CaF$_2$ luminescence, covering radioluminescence, photoluminescence, thermoluminescence, and afterglow. Using synchrotron x-ray excitation together with a cryo-vacuum system, we resolve the thermal quenching of the self-trapped exciton (STE) scintillation into its triplet and singlet components, identify eleven thermoluminescence glow peaks together with their associated emission bands, and separate the temperature-dependent components that make up the long-lived afterglow. The trap depths obtained in this way are closely correlated with the temperature dependence of x-ray-induced isomer quenching, including the enhanced isomer yield near \SI{-60}{\celsius} and the minimum near \SI{-80}{\celsius}, supporting the carrier-trapping picture in which trapped carriers are unavailable to quench the nucleus. Taken together, these results connect the optical and nuclear observables of $^{229}$Th:CaF$_2$ through a unified picture of electron defects and Th-related traps, while providing a comprehensive characterization of the material relevant to solid-state nuclear clock operation.
Source: arXiv (Cornell University)
Authors: Guan, Ming, Bartokos, Michael, Beeks, Kjeld, Hiraki, Takahiro, Kitao, Shinji, Masuda, Takahiko, Nagasawa, Nobumoto, Okai, Koichi, Ogake, Ryoichiro, Pimon, Martin, Sasao, Noboru, Schaden, Fabian, Schumm, Thorsten, Seto, Makoto, Tamasaku, Kenji, Takatori, Sayuri, Yoda, Yoshitaka, Yoshimi, Akihiro, Yoshimura, Koji
Institutions: Okayama University, Innovation Academy for Precision Measurement Science and Technology, CAS, Research Institute for Interdisciplinary Science, Okayama University, TU Wien, Kyoto University, Institute for Integrated Radiation and Nuclear Science, Kyoto University, Japan Synchrotron Radiation Research Institute, SPring-8, RIKEN, The University of Osaka
Language: English
Subfield: Radiation
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7215123104